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Small DC Fan Question

Discussion in 'Electronic Repair' started by Bennett Price, Apr 19, 2008.

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  1. I've got a small 12V DC .9 Watt 'muffin' fan (1.75"x1.75"x3/8").
    It was the cooler for a video card's processor chip and was
    frozen up.

    I put a drop of oil into its sleeve bearing and it now runs
    reliably - almost. It will start every time as long as it is
    not oriented with the open 'face' down. (The open face is the
    side in which you can see the bearing). If the open bearing is
    down, it sometimes starts and sometimes needs a slight nudge to
    get it going.

    What's going on? How come? TIA

  2. Presumably because the bearings are worn out. Get another one.

  3. James Sweet

    James Sweet Guest

    The bearing may be a bit loose. I've had some success disassembling these
    fans, cleaning out the dried up muck, and putting on fresh oil then
    reassemble. It's better to replace it, but if you need to use the computer
    and don't have one on hand, it works in a pinch.
  4. UCLAN

    UCLAN Guest

    What voltage are you applying to it?
  5. jakdedert

    jakdedert Guest

    You oiled it, but you didn't get the gunk off the shaft. When the fan
    is oriented face down there is enough endplay in the shaft for the bit
    of gunk left on it to bind in the bearing. When it's face-up, that part
    of the shaft is likely outside of the bushing.

    When doing these, I usually operate them briefly with some kind of
    solvent, until they run freely again. Then I flush the bearing with
    that solvent--blow as much of it out as possible--THEN relube with 3 in
    1 type oil.

    Sometimes I also pack the open space with a bit of cheap grease before
    resealing...figuring that if the bearing starts to get hot because of
    binding, some of that grease will liquefy and and replenish the bearing.
    I don't know if that's valid, but I usually get good life out of the

    OTOH, fans are cheap and readily available...much cheaper than the stuff
    they protect.

  6. Anywhere from 9 to 15 volts. At 9 it will run in every other position,
    at 15 vdc in the face down position it will still need a nudge.
  7. Jamie

    Jamie Guest

    chances are you have a pressed in race for the bearing.
    you maybe able to tap it in deeper if you can get to it."
  8. I've disassembled these, cleaned, and relubed with decent success.

    But a new fan is not expensive.

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  9. Yes, not nearly as expensive as the possible damage caused by a stalled worn
    out fan that soemone tried to bodge back to working condition instead of
    replacing it. I'm thinking Power Amps, computer chips, or any gear that
    someone has paid you to fix properly.


  10. James Sweet

    James Sweet Guest

    Doesn't sound like anyone has paid him to fix it, the assumption is that
    it's his own stuff that he's fixing himself. I've been known to repair these
    little fans so I can keep using my PC until I can find a suitable
    replacement. Some graphics chipsets use oddball custom heatsink/fan
    assemblies that are difficult to find replacements for.
  11. default

    default Guest

    Realizing that this comes under the heading of "beating a dead horse .
    .. ."

    Only one continuous long bearing supports the shaft? Some have two
    sleeves and you can only see one if you pull the label off - you also
    have to pull the shaft completely out.

    I've had the same experiences with sintered bearings - the sleeve is
    porous and a drop of lube doesn't really do much. The thing worked
    for years and has a particles of grunge and a residue of dried oil
    filling the lubricating channels in the metal.

    If the sleeves can be removed, a cleaning with an ultrasonic cleaner
    and some thin petroleum solvent (mindful of the hazards there) will do
    wonders if the surface is still round (and if you don't see scoring it
    probably is) - then heat the sleeve to 250 F, let it soak at that temp
    for an hour, and drop it into lubricating oil to cool to room temp
    before replacing.
  12. Thanks to all who have responded. I immediately replaced the fan with
    another one - had to devise a way to mount it on the video card heat
    sink which wasn't straightforward. I was just curious about why the fan
    was so position sensitive.
  13. GregS

    GregS Guest

    Sleeves slide around, ball bearing fans seem spring loaded, so position
    is less important.

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